This invention relates, in general, to equipment for performing maintenance operations on steam generators, and in particular, to a multiple port apparatus for delivering a probe into the tube bundle of a steam generator. The invention was conceived particularly with a view towards nuclear-powered steam generators, and many references herein are to that particular application, but it should be clearly understood that the invention is applicable to a wide variety of steam generators and heat exchangers generally, not just those which are nuclear-powered.
A steam generator typically comprises a vertically oriented vessel, a plurality of U-shaped tubes disposed in the vessel so as to form a U-shaped tube bundle, and a tube sheet for supporting the tubes at the ends opposite the U-shaped curvature. The tubes are tightly spaced and arranged in a matrix configuration, forming intertube lanes which are often less than 0.5 inches in width. A central internal division, known as a no-tube lane, is formed between hot and cold legs of the tube bundle. In a nuclear-powered steam generator, for example, the primary fluid used, generally heavy water, is heated by the core of a nuclear reactor as the fluid passes through the tube bundle, and secondary fluid, usually regular water, is fed into the spacing surrounding the tubes. The heat transfer from the hot tubes to the regular water creates steam. The constant high temperature and severe operating conditions result in the formation of deposits and accumulation of sludge on the tubes, tubesheet, and other internal components of the steam generator. These can cause blockages of the internal spacing which results in oscillation of the steam generator, and corrosion of the tubes. This results in decreased efficiency of the heat transfer, and in the case of nuclear-powered steam generators, can result in leakage of heavy water into the regular water. Steam generators thus require regular internal inspection to assess their condition, and cleaning to remove the harmful sludge and deposits.
Existing procedures for maintaining a steam generator generally involve probes which perform a variety of operations inside the tube bundle, including waterlancing, inspection, sampling and retrieval. The probes are designed to be slender to perform within the restrictions of the intertube lane dimensions, and are directed into the tube bundle by a delivery system, which enters the steam generator through openings in the shell of the steam generator. Such openings generally are access holes which are threaded to enable sealing for operation, and are thus appropriate for attaching probe delivery equipment. Inside the steam generator, the delivery system occupies the no-tube lane or the annulus for accessing the tube bundle, and utilizes a device for directing the probe into the desired location in the bundle.
U.S. Pat. No. 4,407,236, entitled "Sludge lance for nuclear steam generators", describes guide diverter structure portions for delivering a lance into the tube bundle of a steam generator. U.S. Pat. No. 4,424,769, entitled "Process and apparatus for removal of the sludge deposits on the tubesheet of a steam generator", describes a drive for feeding a lance into or out of a steam generator tube bundle directly through an access hole. U.S. Pat. No. 4,638,667, entitled "Remote probe positioning apparatus", describes a telescopic boom and a tractor feed and deflector block apparatus for delivering a probe into the tube bundle of a steam generator. U.S. Pat. No. 4,980,120 entitled "Articulated sludge lance", describes a guide and an articulated mechanism for delivering a lance into the tube bundle of a steam generator. U.S. Pat. No. 5,065,703 entitled "Flexible lance for steam generator secondary side sludge removal", describes a transport apparatus for delivering a lance into the tube bundle of a steam generator. U.S. Pat. No. 5,341,406 entitled "Sludge lance guide flexible lance system", describes a support rail, a rigid guide, and a lance guide nose apparatus for delivering a lance into the tube bundle of a steam generator. U.S. Pat. No. 5,411,043 entitled "Articulated annular sludge lance", describes track members, a manipulator head, a delivery rail, and a flexible manipulator for delivering a lance into the tube bundle of a steam generator.
The existing systems suffer from the disadvantages of being difficult to operate in confined spaces, and particularly in steam generators with restricted access. As a result the systems lack optimum precision for locating and directing the probe, and lack optimum protection of the probe during operation. There is thus a need for a probe delivery system which lends itself to operation in confined spaces for improved precision of location and directional control of the probe, and also having suitable protection for the probe during operation.